Description: (provided by the applicant) Age-related osteoporosis is characterized by decreased osteoblast number and bone forming activity, and increased bone marrow adipocyte content. This suggests a shift in bone marrow mesenchymal stem cell (MSC) differentiation pathways, with increased adipocyte and decreased osteoblast production. The mechanisms underlying these changes have not been defined. Recently, our laboratory has demonstrated that lipid oxidation products (LOPs) inhibit the differentiation of preosteoblastic cells into osteoblasts and promote their adipogenic differentiation in vitro, in parallel with altered responsiveness to bone morphogenic protein-2 (BMP2) and other bone-growth factors. Moreover, mice fed an atherogenic high-fat diet exhibited decreased bone mineral density (BMD) and a reduced capacity of their MSCs to differentiate into osteoblastic cells in vitro. Therefore, it is hypothesized that LOPs contribute to age-related osteoporotic bone loss by decreasing bone cell growth factor production and/or responsiveness, and enhancing adipogenic differentiation of bone marrow stem cells at the expense of osteoblast production. To examine this hypothesis, we will pursue the following specific aims: 1) further characterize the in-vivo effects of high-fat diet on bone resorption and formation as assessed by quantitative bone histomorphometry, bone turnover markers, and changes in bone mass, in parallel with measurements of serum and bone LOP levels and indices of calcium and vitamin D metabolism; 2) examine the in-vivo effects of high-fat diet on bone marrow stem cell adipogenic (PPARg, aP2, and lipoprotein lipase)and osteoblastic (bone-associated alkaline phosphatase and osteocalcin) gene expression and phenotype; 3 ) determine whether treatment with the dietary antioxidant lutein can inhibit the adverse effects of high-fat diet on bone marrow stem cell differentiation, as assessed by effects on bone histomorphometry and adipocyte vs osteoblast specific gene expression; and 4) further define the in-vivo and direct in-vitro effects of LOPs on osteoblast and osteoblast precursor expression of, and responsiveness to, key bone growth factors including TGF-a, IGF-I/1I and BMP-2/4. In particular, we will pursue our recent observation that LOPs both inhibit BMP2 stimulation of marrow stem cell osteoblastic differentiation and promote adipogenesis in vitro, by examining the mechanisms of this effect in terms of changes in BMP2 type IA and lB receptor expression and second messenger generation. It is anticipated that these studies will identify new targets for interventions to prevent and treat age-related osteoporosis.